This invention relates generally to a device which enters changes in a measured quantity as changes in an electric signal and uses a displayer to give a warning at a specified value or to display the measured value. It relates in particular to a measuring device which provides a fluctuation-suppressing means between the input and output circuits to suppress the fluctuations in its display caused by irregular variations in the measured quantity.
A fuel gauge for a vehicle equipped with a delay circuit for suppressing fluctuations, for example, may be considered as an analog device or a digital device.
Firstly, there is shown in FIG. 1 a mechanism for making an analog display of the remaining amount of fuel. The resistance of a rheostat 1 is caused to change according to the variations in the vertical position of the liquid surface and it is used to detect the liquid level as a variation in the terminal voltage. This is entered into a driving circuit 3 through a delay circuit 2 consisting of a resistor and a capacitor so that an ammeter 4 is activated as an indicator for an analog display of the amount of remaining fuel.
In this application, vibrations of the vehicle will cause big changes in the liquid surface and the terminal voltage of the rheostat unit 1 will correspondingly undergo unstable variations but such abrupt changes are absorbed by the delay circuit 2 so that a relatively stable display can be obtained by the ammeter 4.
FIG. 2 shows, on the other hand, an example of measuring and displaying the remaining amount of fuel by a digital processing. In this example, the output voltage which corresponds to the liquid level and is detected by the rheostat unit 5 is converted into a digital signal through an A-D conversion circuit 6 and is transmitted as a display signal to a digital displayer 8 by a decoder driver 7. Since it is indispensable also in this situation that liquid surface variations be absorbed, a delay circuit as shown in FIG. 1 may be connected to the output side of the voltage terminal of the rheostat unit 5, but a delay circuit 9 for absorbing the variations of digital quantity is provided at the back side of the A-D conversion circuit 6 in the case of such a digital processing. Such variation-absorbing function of digital processing is particularly useful for calculation display by a microcomputer because it is customary and structurally advantageous to incorporate the delay circuit 9 inside the system.
If it is desired to detect the lowering fuel level and to activate an alarm at a predetermined point, a judgment circuit may be installed for comparing the standard voltage corresponding to the alarm-activating point and the input voltage (the digital signal corresponding to the alarm-activating point and that corresponding to the input voltage after the A-D conversion) so that the alarm will be activated by this judgment signal. In this situation, too, since the variations in the liquid surface at the alarm-activating point give rise to chattering in the judgment signal, it is necessary to prevent the unstable behavior of the alarm by means of a delay function as described above for the case of ordinary displays.
Since these delay functions for absorbing variations operate unconditionally in response to input signals, however, they are disadvantageous when used, for example, for checking the input/output characteristics for the inspection of such display devices at the time of delivery from factory or for their diagnostic testing because the output will not easily reach the value corresponding to the input due to the delay function even if the input is changed to one of a certain number of typical values (inclusive of the alarm-activating level). This makes inspections and diagnostic testing very time-consuming.
If, as in the case of a microcomputer, all processing functions except for the input and output circuits are incorporated into one IC, it is desirable from the point of view of cost to incorporate internally the processing functions which are used in common so that the device can be made usable with a large variety of measuring instruments merely by replacing the input and output circuits. If the aforementioned delay function is incorporated, however, there arises the problem that the same IC can no longer be used for the measurement not requiring a delaying process such as the detection of the voltage of a battery and that dedicated ICs incorporating individual processing functions must be provided.